The present invention relates to a printing offset blanket. More particularly, it relates to a printing offset blanket which is suitable for rotary offset printing used for news printing.
In general, an offset blanket used for rotary offset printing has a structure wherein a surface printing layer 11 is laminated on a supporting layer 12, as shown in FIG. 5. The supporting layer 12 is formed, for example, by laminating a plurality of supporting base layers 13 obtained by impregnating a supporting base with a rubber material (rubber cement) (normally, three or more cotton fabrics are laminated to each other), providing at least one compressive layer 14 on the supporting base layer and further laminating a reinforcing layer 15 on the surface of the compressive layer. The reinforcing layer 15 is that obtained by impregnating a woven fabric such as cotton, polyester, rayon, etc. with the same rubber material as that used in the above supporting base layer 13.
The reinforcing layer 15 plays a role in inhibiting the surface printing layer 11 from being shifted in a rotational direction at the time of printing to prevent misregister of printing, and the role in enhancing a pressure to be applied on the surface of the blanket at the time of printing to improve solid inking properties. Therefore, a conventional offset blanket is always provided with the reinforcing layer 15.
However, in offset printing using a conventional offset blanket as shown in FIG. 5, pressure absorption due to the compressive layer 14 is not sufficiently conducted when pressure is applied on the blanket 16 by an impression cylinder 17, as shown in FIG. 6, because the reinforcing layer 15 is disposed between the surface printing layer 11 and the compressive layer 14. Thereby, a so-called bulge 18 is formed in the blanket which is in contact with the impression cylinder 17.
When a bulge 18 is formed, the perimeter (length of the surface) of the blanket 16 is increased and the amount of paper fed per one rotation becomes larger, which results in a decrease in the paper's tension after it has passed through the blanket 16. As a result, the paper becomes slack between units in rotary offset printing.
Particularly, in rotary offset printing used for news printing, poor tension between B/B (Blanket to Blanket unit) and satellite (color printing unit) greatly influences the quality and workability of the printing. More concretely, paper slack due to an increase in the length of the perimeter of the blanket 16 causes printing defects, such as poor paper-feed, misregister, double images, etc.
On the other hand, the above problem can be solved by eliminating the reinforcing layer 15 from the offset blanket 16. However, it is impossible to inhibit the surface printing layer 11 from being shifted in a rotational direction by only eliminating the reinforcing layer 15. This shift results in formation of misregister and deterioration of solid inking properties.